In essence, these are bets on which way the oil price will move. Since the real currency of such contracts is cash, rather than barrels of crude, there is no limit to the number of bets that can be made. And since no oil is ever held back from the market, these bets do not affect the price of oil any more than bets on a football match affect the result.
The going after oil speculators resambles just how inoperative the government really is, regarding high oil prices.